The present invention relates to hot-swap protection circuitry generally.
Various types of hot-swap protection circuitry are known in the patent literature. The following U.S. Patents are believed to represent the state of the art: 5,530,302 and 5,317,697.
Hot-swap protection circuitry may be understood as including circuitry which enables electronic circuits to be connected to each other and disconnected from each other while under voltage. Hot-swap protection circuitry is required in many applications where it is not practical to shut-down an electronic system while replacing certain circuit boards thereof. Examples of such systems are telephone switches as well as computers. For example, the insertion and removal of PCMCIA cards is normally carried out under voltage, when the computer is turned on.
Conventional hot-swap protection circuits employ non-standard connectors which include at least one of an extra long pin and an extra-short pin, connected to voltage detectors, so that immediately upon connection and/or disconnection, the presence and/or the absence of voltage can be immediately sensed.
The present invention seeks to provide an improved hot-swap protection circuit which does not require the aforesaid non-standard connectors of the prior art.
There is thus provided in accordance with a preferred embodiment of the present invention an electronic hot-swap protection circuit for enabling hot swap connections and disconnections, the circuit including:
a detector for detecting electrical current or voltage along a conductor which supplies power to a circuit to be protected during hot swap connections and disconnections; and
a fast-disconnect, slow-reconnect switch connected in series with the detector and being operative in response to an output thereof, whereby the switch is relatively quickly opened when the absence of current is detected while the switch was closed and the switch is relatively slowly closed when voltage is detected following opening of the switch.
Preferably, the fast disconnect, slow-reconnect switch comprises a FET.
In accordance with a preferred embodiment of the present invention, the detector operates by sensing a polarity change.
Preferably, the detector operates by sensing a polarity change across the FET.
In accordance with a preferred embodiment of the present invention the detector is operative to provide a hot-swap occurrence indication to the circuit to be protected.
Preferably, the detector and the fast-disconnect, slow-reconnect switch also operate together as a low-pass filter.
In accordance with a preferred embodiment of the present invention, the low-pass filter has a voltage drop thereacross which is set by the detector.
Preferably, the detector comprises a control circuit.